Use of the hexagonal phase of the compound (fe, co)2p in particle size permanent magnets



June 8, 1965 K. J. DE vos ETAL 3,188,247 USE OF THE HEXAGONAL PHASE OFTHE COMPOUND (FE, co) 1 IN PARTICLE SIZE PERMANENT mum's Filed Oct. 29,1962 2 Sheets-Sheet 1 HEXAGONAL ORTHORHOM BIC Temperature ("C) m d 8Curie Poir 1t(C) FIG.2

INVENTORS xnun 4 DE ms AGEZT I June 8,1965

Filed Oct. 29. 1962 Hc (Oerst-e d5) K. J. DE vos ETAL 3,188,247

USE OF THE HEXAGONAL PHASE OF THE COMPOUND (FE 00):? IN

PARTICLE SIZE PERMANENT MAGNETS 2 Sheets-Sheet 2 Fe Cc Fe/Co Ratio emvrsmons C0 mam)! I De Vos ELMUJ AJFJZ vewc W's-Z051. 6. vmvocrsrte-AGENT FIGJ United States Patent 9- s 188 247 USE OF THE HExAGoNAL PHASEon THE coM- POUND (Fe,Co) P IN PARTICLE SIZE PERMA- NENT MAGNETS Krijn.lacobus de Vos, Wilhelmns Antonius Johannes Josephus Velge, and MichaelGottfried van der Steeg, Emmasingel, Eindhoven, Netherlands, assignorsto North American Philips Company, Inc., New York, N.Y., a corporationof Delaware Filed Oct. 29, 1962, Ser. No. 233,526

6 Claims. (Cl.-148101) 'August 14, 1961, which states that the (Fe,Co)P-parti'- cles with an Fe/Co ratio up to 80:20 may be fully in one phasewith the hexagonal Fe P structure at room temperature. particles havingan Fe/Co'ratio ofless than 80:20, particularly (Fe,Co) P-particleshaving an Fe/Co ratio up to- 60:40, may still contain the hexagonalphase and thus are suitable for the manufacture of permanent magnets.

. We have found that the permanent magnetic properties and Curie pointof such magnets are deleteriously affected by the formation at the lowertemperatures of the V orthorhombic phase and, in accordance with theinvention,

these difficulties are overcome by means of a'rapid cooling of theparticles at rates which depend upon the cobalt content and overtemperature ranges whose upper limit depends upon the Fe/Co ratio, tothereby suppress the formation of such a phase.

In order that our invention may be clearly understood and readily putinto effect we shall describe the same in more detail in reference toseveral specific examples and to the accompanying drawing which:

FIGURE 1 is a constitutional diagram of the quasibinary section Fe P-CoP.

FIG. 2 is a diagram showing Curie points of various alloys with thehexagonal and orthorhombic phases.

FIG. 3 is a graph showing for various alloys minimum cooling ratesaccording to the invention, and

FIG. 4 is a graph showing the coercive force at room temperature ofFe,Co/ P particles made by our method before and after heating.

From FIGURE 1, which was obtained by differential thenno-analysis andX-ray examination, it is seen that the hexagonal phase in thequasi-binary section between Fe 'P and Co P of the ternaryconstitutional diagram Fe-Co-P probably extends, at high temperature, asfar as compound Co P itself. FIGURE 1 also shows that the hexagonalphase of (Fe,Co P), which is stable at the higher temperatures, passesat lower temperatures into another phase which can be described as theorthorhombic phase, and that the transition temperature varies with thecomposition.

As shown in FIGURE 2, in which curve A represents the hexagonal phaseand curve B represents the orthorhombic phase it is seen that theorthorhombic phase, which 'is also ferromagnetic, has a Curie pointwhich is lower than that of the hexagonal phase. We have found that thepresence at room temperature, of this orthorhombic phase with thehexagonal phase adversely affects the permanent magnetic properties ofthe ferromagnetic particles, especially reduces the coercive force whichintum reduces the BH value.

This application further states that the (Fe,Co) P- 3,188,247 Patented.June 8, 1965 below about 600 C. The cooling is carried out at an averagerate which varies with the cobalt content and increases according as thecobalt content increases, with the understanding that for alloys havinga Fe/Co ratio of 90:10, the cooling rate must be at least about 2C./sec.

and for the alloys having a Fe/ Co ratio of between :25 and 60:40, thisratio should exceed about 75 C./sec.

FIGURE 3 shows the minimum average'cooling rates between about 1200 C.and about 600 C. for the various alloys as a function of the Fe/Coratio.

So far we have not succeeded in quenching (Fe,Co) P-' alloys having anFe/Co ratio of less vthan 60:40 so rapidly that, at room temperature,they consist substantially completely of the hexagonal phase.

The coercive force of the (Fe,Co) P-particles cooled down in the mannerof our invention may be'even further increased by heating the particlesin a non-oxidizing atmosphere at a temperature preferably lying below650 C. for a period of time which increases as the temperature liesfurther below 650 C. For reasons of diffusion velocity, the lowestheating temperature should not be less than about 300 C. Theseheat-treatments are ef fected in the range in which the orthorhombicphase is stable. Therefore, when the heat-treatment is of too longduration, the orthorhombic phase occurs again beside the hexagonalphase, as a result of which the coercive force may decrease again. If aheating temperature higher than 650 C. is used this results in adecrease of the coercive force even with heat-treatments of very shortduration. Therefore, the highest heating temperature should preferablynot exceed 650 C.-

We have found that, as shown between the broken lines in FIG. 4, amaximum occurs in the coerciveforce, particularly for the particleshaving Fe/Co ratio of between 10 and 80:20, both after cooling from therange of the hexagonal phase and after the heat-treatment at atemperature lying between 650 C. and 300 C. The maximum increase of thecoercive force is obtained if the (Fe,Co) P-par-tic1es, after havingbeen cooled down, are heated in a temperature range between about 400 C.and 500 C. Referring to FIG. 4, curve C shows the coercive force at roomtemperature for (Fe,Co) P-particles immediately after they have beencooled down from a high temperature at a rate of approximately C./sec.,and curve D shows the coercive force of such particles after beingsubjected to heat-treatment at a temperature lying between 400 C. and500 C.

, The (Fe,Co) P-particles may be compressed, if desired,

in a magnetic field, to form a composite magnet body. It has been foundthat the coercive force of the particles is adversely alfected by stressin general and consequently also by the compression. This decrease ofthe coercive force of the particles which have been subjected to stressmay be wholly or partly eliminated by subjecting the particles again toa heat-treatment in the temperature range lying below 650 C., asdescribed hereinbefore. It is not necessary for the cooled (Fe,Co)P-particles to be previously heated in the temperature range lyingbetween 650 C. and 300 C. and then compressed, for example, to form amagnet body and finally heated again in the said temperature range,butthe particles may be compressed, if desired in a magnetic field, toform a magnet body immediately after being cooled down and subsequentlyheated in the temperature range lying between 650 C. and 300 C. Thecoercive force in this case also increases to a value which differs onlyslightly from that of the particles treated in accordance with thefirst-mentioned method.

Example I A melt was formed of 95 by weight of phosphorouscopper, 4.25%by weight of iron and 0.75% by weight of cobalt containing (Fe,Co)P-particles having a Fe/Co. ratio of 85:15. This melt was cooled down inaccordance with the invention at an average rate exceeding the requiredminimum average rate of approximately C./ see. (see FIG. 3), i.e., at arate of approximately 100 C./sec. and the coercive force of theparticles at room temperature was found to be 685 oersteds. According tothe X-ray diagram such particles consist entirely of the hexagonal phaseof the Fe P-structure. When the melt was cooled down at an average ratelower than the required minimum average rate of approximately 5 C./ sec.at room temperature a coercive force of only 25 oersteds was obtainedand the particles consisted, accord ing to the X-ray diagram, of twophases, viz. the hexagonal phase, and the orthorhombic phase. Thisclearly proves the unfavourable influence of the orthorhombic phase onthe coercive force.

Example 2 A melt was formed of 95% by weight of phosphoruscopper, 3.5%by weight of iron and 1.5% by weightof cobalt containing (Fe,Co)P-particles having a Fe/Co ratio of 70:30. This melt was cooled inaccordance with the invention'at an average rate higher than therequired minimum average rate of approximately 130 C./sec. (see FIG. 3),i.e., at an average rate of approximately 200 C./sec. The coercive forceof the particles at room temperature was found to be 275 oersteds andthe particles consisted substantially completely of the hexagonal phase.When the melt was cooled down at an average rate of 40 C./sec., i.e., atan average rate below the required minimum average rate, the coerciveforce at room temperature wasfound to be only 143 oersteds and theparticles consisted of the hexagonal and orthorhombic phases.

Example 3 A melt was formed of 95% by-weight of phosphoruscopper, 3.75%by weight of iron and 1.25% by weight of cobalt containing (Fe,Co)P-particles having a Fe/Co ratio of 75:25. After the melt was cooleddown at an average rate higher than the required minimum average rate ofapproximately 75 C./sec. (see FIG. 3), i.e., an average rate ofapproximately 200 C./sec. the coercive force at room temperature wasfound to be 735 oersteds and the particles consisted completely of thehexagonal phase. After cooling down at an average rate of 40 C./ see,i.e., an average rate lower thanthe required minimum average rate, theparticles were found to consist of both the hexagonal and orthorhombicphases and the coercive force at room temperature was only about 326oersteds.

Example 4 A melt was formed of 99% by weight of phosphoruscopper, 0.85%by weight of iron and 0.15% by weight of approximately 70%. After thecompression treatment the magnet was heated again for 2 hours at 400 C.and was found to have the following magnetic properties: B =3950 gauss,11 :2400 oersteds, 11 1920 oersteds and BH =3J 10 gauss-oersteds. i

While we have described our invention in connection with specificexamples we do not desire to be limited thereto as obvious modificationswill readily present themselves to one skilled in this art.

What is claimed is:

1. In the manufacture of permanent magnets from separate particle-sizemagnets containing the hexagonal phase of the compound (Fe,Co)- P as theconstituent essential for the permanent magnetic properties, heatingsaid particle-size magnets with a Fe/Co ratio between about :10 and60:40 to a temperature at least between 900 C. and 1150 C., and coolingsaid particle-size magnets to a temperature below about 600 C. from saidtemperature a such an average rate greater than about 2 C./sec. as toprevent the formation at the lower temperatures of the orthorhombicphase.

2. In the manufacture of permanent magnets from separate particle-sizemagnets containing the hexagonal phase of the compound (Fe,Co) P as theconstituent essential for the permanent magnetic properties, heatingsaid particle-size magnets with a Fe/Co ratio between about 90: 10 and60:40 to a temperature at least between about 900 C. and 1150 C. andwhich increases with decreasing values of said ratio, and cooling saidparticle-size magnets to a temperature below about 600 C. from saidtemperature with an average cooling rate which increases with a decreasein said ratio and which is at least 2 C./ sec. when said ratio is about90:10 and greater than 75 C./sec. when said ratio is between about 75-25and 60:40.

3. In the manufacture of permanent magnets from separate particle-sizemagnets containing the hexagonal phase of the compound (Fe,Co) P as theconstituent essential for the permanent magnetic properties, heatingsaid particle-size magnets with a Fe/Co ratio between about 90: 10 and60:40 to a temperature at least between about 900 C. and 1150 C. andwhich increases with decreasing values of said ratio, cooling saidparticle-size magnets to a temperature below about 600 C. from saidtemperature with an average cooling rate which increases with a decreasein said ratio and which is at least 2 C./sec. when said ratio is about90:10 and greater than 75 C./sec. when said ratio is between 75:25 and60:40, and heating said particle-size magnets in a non-oxidizingatmosphere at a temperature between about 650 C. and 300 C. for a timewhich is higher as the heating temperature is selected lower.

4.The method of claim 3 in which the heat-treated particle-size magnetsare pressed into an adherent magnet body and the body is heated in anon-oxidizing atmosphere at a temperature between about 650 C. and 300C.

5. In the manufacture of permanent magnets from separate particle-sizemagnets containing the hexagonal phase of the compound (Fe,Co) P as theconstituent essential for the permanent magnetic properties, heatingsaid particle-size magnets with a Fe/Co ratio between about 90:10 and60:40 to a temperature at least between about 900 C. and 1150 C. andwhich increases with decreasing values of said ratio, and cooling saidparticle-size magnets to a temperature below about 600 C. from saidtemperature with an average cooling rate which increases with a decreasein said ratio and is at least 2 C./sec. when said ratio is about 90:10and greater than 75 C./ sec. when said ratio is between 75:25 and 60:40,pressing said particle-size magnets into an adherent body, and heatingthe body in a non-oxidizing atmosphere at a temperature between about650 C. and 300 C.

6. The method of claim 5 in which the particle-size magnets are pressedin the presence of a magnetic field.

(References on following page) 5 6 References Cited by the Examiner vOTHER REFERENCES UNITED STATES PATENTS Archiv fur das Eisenhuttenwesen,22 Jahrgang, March! V 2,190,667. 2/40 Kelsall et a1. 148-401 April 9(Pages 131-135 "lied 2,207,685 7/40 Russell et a1. 148-101 5 D V L.RECK, Primary Examiner.

2,245,477 6/41 Jonas 148-101

1. IN A MANUFACTURE OF PERMANENT MAGNETS FROM SEPARATE PARTICLE-SIZEMAGNETS CONTAINING THE BEXAGONAL PHASE OF THE COMPOUND (FE,CO)2P AS THECONSTITUTENT ESSENTIAL FOR THE PERMANENT MAGNETIC PROPERTIES, HEATINGSAID PARTICLE-SIZE MAGNETS WITH A FE/CO RATIO BETWEEN ABOUT 90:10 AND60:40 TO A TEMPERATURE AT LEAST BETWEEN 900*C. AND 1150*C., AND COOLINGSAID PARTICLE-SIZE MAGNETS TO A TEMPERATURE BELOW ABOUT 600*C. FROM SAIDTEMPERATURE A SUCH AN AVERAGE RATE GREATER THAN ABOUT 2*C./SEC. AS TOPREVENT THE FORMATION AT THE LOWER TEMPERATURES OF THE ORTHORHOMBICPHASE.